There seems to be a lot of confusion out there regarding ski terms, whether it be geometry, construction, mounting, or other jargon, and as a result there are a lot of unnecessary threads clouding up gear talk that could be answered by simple research and knowledge of ski language. This guide is designed to clarify any confusion based on different terms people use when describing skis, bindings, boots, or whatever, and to illustrate the uses of basic ski features/design. A lot of these are really basic, the kind of stuff everyone on this site knows, while others are much more confusing to people, even though they may seem simple in principle.
Camber: Camber is a design characteristic used to improve a ski's performance on hard, 2 dimensional snow. If you were to take a pair of fully cambered skis and put the bases together, there would be two contact points; one right at the tip and one right at the tail, with a gap in between the middle area of the skis. The idea behind camber is that when you click in and are standing on a pair of cambered skis, 100% of the base is in contact with the snow, but there is greater pressure on the tip and tail of the ski than the middle. When the ski is rolled on edge, the tip (or tail if skiing switch) is forced into the snow with greater weight than the middle of the ski, which helps with turn initiation. This is why a ski with full camber will carve more easily than a ski with a flat base (i.e. k2 domain/revival) or a rockered ski. Camber unfortunately detracts from a ski's performance in 3 dimensional snow (like powder, chop, windblown, etc.) because the greater pressure on the tip and tail that help the ski's performance in hard snow force the tip down, sinking the ski and causing it to drag and eventually throw the skier on his/her face (tip dive).
Rocker/Reverse Camber: Rocker is a design characteristic that was initially invented to help skis float in 3 dimensional snow (it was adapted from water skis). If you were to put a pair of full reverse camber skis together with the bases touching, the skis would only touch right under the binding, with the tails and tips separated. Reverse camber refers to a full continuous curve of the ski, where the only contact point is right under the boot. Rocker refers to an elevated, early rising tip and/or tail, although the two terms are used pretty much interchangeably. Rocker in a ski puts less pressure on the tip than on the midfoot of a ski, causing the tip to rise up to the surface of 3 dimensional snow. Recently, it has been used in park or all mountain skis to reduce catching on rails or in crud, although this makes turn initiation slightly slower on hardpack.
Sidecut: The sidecut of a ski refers to the curve of a ski's side. On a traditional parabolic ski, the tip and tail are the widest points in a ski forward and rearward of the center, respectively. The sidecut is the continuous curve from the tip to the waist to the tail. Companies will refer to their skis' sidecut in quantified fashion using the term 'turn radius'. A ski's turn radius is if you took the sidecut curve from the widest point in the tip through the waist and through the tail, and continued that curve until it made a full circle. The radius of that circle would be the turn radius of the ski. Essentially, the longer the turn radius, the longer the turn the ski is most comfortable making. For example, the Armada JJ has an extremely short radius (14 meters or so). Because of this, the ski is very comfortable making short turns and turning sharply. At high speeds, this radius works against the ski and makes it want to hook and turn sharply unexpectedly, causing it to be slightly unstable at speed. Conversely, the 4frnt EHP has a hybrid 45 meter and 60 meter turn radius in the 193 cm size. This is essentially a straight sidecut, and makes the ski very stable making long turns at high speeds, but as a result, the ski may feel sluggish making short turns.
Reverse Sidecut/Taper: Reverse sidecut or taper refers to the widest point of the ski in the tip and/or tail being moved closer to the binding area. A full reverse sidecut has the widest point of the ski in the center of the boot, with everything outward from there getting narrower. The idea behind this design feature is that it reduces drag and allows the ski to pivot more quickly in 3 dimensional snow. When a traditional parabolic ski is laid on edge in deep snow, the tip and tail sit deeper in the snow collumn than the middle of the ski, causing them to drag and push against the snow. A full reverse sidecut ski laid on edge in deep snow will have the deepest area of the ski in the middle, with the tip and tail higher up in the snow collumn, which reduces drag and allows the tips and tails to slide through the snow more efficiently. The downside to a full reverse sidecut is it completely negates the ability to carve on 2 dimensional hard pack snow, and is pretty soft snow specific. A hybrid taper/standard sidecut ski (like the Armada JJ, Salomon Rocker 2, and Atomic Bent Chetler) will allow a ski to pivot more quickly than a traditional ski in deep snow, while still retaining the ability to carve a turn on hardpack.
Pintail: A pintail design refers to a ski with a tapered tail that is at most 10mm wider than the waist measurement, and with a tip that is significantly wider than both. This is a very directional shape which excels in deep snow (going forwards) by allowing the tail to sink, which raises the tip and increases the ski's ability to plane and turn quickly when things get deep. The classic pintailed ski is the K2 Pontoon, designed by the legendary Shane McConkey. This is a very unidirectional design because the tail is designed to sink, which floats the tip when going forwards. Riding a pintail switch in deep powder, the tail would immediately sink, throwing the skier on his/her ass.
Sidewall vs. Cap: Sidewall refers to a strip of material, generally ABS or UHMW plastic, situated directly over a ski's edge. This material reinforces the edge, and dampens the ski, allowing for a more stable ride. Cap construction refers to a ski with a fibercap that wraps around the topsheet and down the sides of the ski to the edges. This allows for a lighter ski, and is a cheaper construction than sidewall. Generally more expensive, flagship skis have sidewall construction, and entry level skis use a cap construction, although more and more skis are using hybrids of the two to create damp, stable skis that are still very lightweight. Armada and Atomic seem to be fans of hybrid construction. One of the main functional advantages of a sidewall construction is that if a section of sidewall blows out, it can be repaired relatively easily by epoxying in a new piece of ABS or whatever, whereas a blown out cap is much more difficult to fix and often results in a complete delamination of the ski. Different strokes for different folks, although it's generally agreed that sidewalls are a superior construction. That's not to say there aren't great cap skis (line invader, anthem), or shitty sidewall skis (OG salomon suspects), that was simply referring to the construction.
Base Convexity: This is a relatively new design feature that is being experimented with in which a ski has 'rocker' not running lengthwise, but widthwise (edge to edge). This increases a ski's slarviness and float in soft, 3 dimensional snow, but makes it dangerous and hard to stop in hard conditions. Examples of skis with convex base sections include Gary Wayne skis, the DPS Spoon 150, and the new 2013 On3p Pillowfight (only convex in the rockered sections, flat underfoot). Convexity or concavity can also be a defect, causing a ski to behave erratically on hard snow.
Sintered vs. Extruded Base: A sintered Ptex base will absorb and hold wax longer and more effectively, and when fully waxed will be faster than an extruded base. Extruded bases are cheaper to produce, but lose wax more quickly and tend to be slower. Both have similar durability, although very high quality sintered bases tend to be slightly more fragile than extruded bases or lower quality sintereds. These ultra-fast, high quality sintered bases are called race bases.
Subliminated vs. Die-Cut Base: A die-cut base refers to a base graphic assembled by different sized pieces of colored Ptex being cut out and fit together like a puzzle to form the base graphic. K2 uses die-cut bases on almost all of their skis. Conversely, a sumbliminated base is a base with the graphic printed on a sheet of nylon which sits underneath the base itself, with the Ptex being transparent to show the graphic below. On3p and Moment use subliminated base graphics. Subliminated bases tend to be slightly more durable and chip-resistant than die-cut bases, although the difference is minimal.
Flex: This one is pretty self-explanitory. This refers to a ski's stiffness. A stiff ski will be more stable at speed, while being less playful than a soft ski.
Length/Width: Another simple one. Length of skis is measured in centimeters, with width being measured in millimeters.
Mounting Point: There seems to be quite a bit of confusion regarding mounting point. There are two main terms thrown around regarding a ski's mount: true center and core/chord center. True center refers to the exact center of a ski. Take the length, divide by 2 and you have true center of a ski. Core center refers to the spot on the ski where the core/sidewall is the thickest. On a fully symmetrical ski, true and core center are the same spot. On a directional ski, core center is located back from true center, although it's in a different spot for every ski. There is also factory reccommended, which is generally the center of the ski's sidecut, which usually correlates with core center. When talking about the best place to mount a ski, people generally refer to a spot in relation to either factory recommended or true center. For example, the K2 Hellbent has a factory recommended of -7.5 cm from true center. The 'sweet spot' or ideal mounting spot tends to be further up than that, usually from around true center back to -4 cm or so from true center. For this particular ski, true center is the same thing as +7.5 from factory rec. and -2 from true center is +5.5 from factory rec. and so on. Keep in mind that the factory recommendation is going to be different for every ski, so to avoid confusion it's probably best to refer to a mount in relation to true center.
Binding Types: There are 3 main types of alpine bindings: alpine bindings, alpine touring bindings, and low-tech or randonee bindings. Alpine bindings are just your standard, 'put the toe of your boot under the toe piece and click your heel down and you're good to go.' Examples of alpine bindings are the rossignol fks, salomon sth, tyrolia peak, and marker jester bindings. Alpine touring bindings technically include low-tech bindings, but for the sake of this explanation we'll separate them. Standard alpine touring bindings are bindings you can click into just like a standard alpine binding, but upon flipping a switch or lever, can free the heel for use in skinning cross-country style to get uphill to a zone. Examples of this type of binding include the marker duke, salomon guardian, tyrolia adrenaline, or any standard alpine binding on an mfd plate. Low-tech or randonee bindings are non-compatible with standard alpine boots and are engaged by clicking two small pincers into two small cavities in the sides of a boot's toe. Two pins are engaged into the heel of the boot to secure the heel. The heel of a low-tech binding can either rotate or engage risers that prevent the pins from entering the boot, allowing the user to skin free-heel to a zone. The advantage of a low-tech style binding is their extremely low weight, and the fact that with each step, the user is only lifting his/her boot, as opposed to lifting the entire binding frame, like on a standard alpine touring binding, which results in less leg fatigue. Examples of low-tech bindings are the dynafit vertical ft 12, plum guide, and g3 onyx bindings.
I hope this helps. Feel free to add other terms/definitions that you think would benefit beginning users.